1. Technical Field
The present invention relates to an active matrix display device using an organic EL (Electro-Luminescence: electroluminescence) panel. The invention further relates to an electronic apparatus, etc., using such a display device.
2. Related Art
An organic EL panel is configured by arranging organic light emitting diodes (Organic Light-Emitting Diode: OLED) having a light emitting layer made of an organic compound in a plurality of pixels. Such an organic light emitting diode emits light when molecules of the organic compound, which have been excited by energy, generated by recombination of electrons and holes that are injected into the light emitting layer, return from the excited state to the ground state. In the organic EL panel, application of a current between the anode (positive electrode) and the cathode (negative electrode) of the light emitting diode causes impulse lighting at a brightness corresponding to the current value.
Examples of a method for driving the organic EL panel include the passive matrix type and the active matrix type. According to the passive matrix type, organic light emitting diodes of the respective pixels are connected between a plurality of lines of an anode driver and a plurality of lines of a cathode driver. Although its structure is simple as described above, light is emitted on a line by line basis and therefore brightness of the light emission is required to be high, which leads to problems of short life span of elements and degradation of image quality due to crosstalk.
On the other hand, according to the active matrix type, a plurality of transistors are arranged in each pixel, and high light emission efficiency and high image quality are feasible by applying a current to organic light emitting diodes during a predetermined period. However, use of TFTs (thin film transistors) made of amorphous silicon as the transistors of pixel circuits causes an increase in age-related change, while use of TFTs made of low temperature polycrystal silicon causes an increase in variation in threshold voltage in the pixels. In either case, a complex structure of pixel circuits is needed in order to compensate for such problems.